Yes, I learned the hard way that you have to water them more frequently than anything else--including planters/containers. So I try to remember to wet the soil every day. Just long enough for the water to start dripping out through the drain holes. Petunias do have to be deadheaded otherwise they get very sparse and leggy. I hate that chore, so that's why I replaced most of the petunias with begonias this year.

I also learned that if it rains, I'm not necessarily off the hook for watering. The eaves are not big at all, but big enough to divert the rain water from the boxes.